1. Field of the Invention
The present invention relates to a downhole surge pressure reduction method and apparatus for use in the oil well industry. More particularly, the method and apparatus of the present invention provides surge pressure reduction functionality while running a drilling/production liner or sub-sea casing down a borehole.
2. Description of the Prior Art
U.S. Pat. No. 5,960,881 (xe2x80x9cthe ""881 patentxe2x80x9d), which is incorporated herein by reference and which should be referred to with respect to the advantages provided by that invention, describes the principle of operation of a downhole surge pressure reduction system. The invention of the ""881 patent has provided the oil well industry with the capability of running in a drilling/production liner faster and more reliably with a minimum of lost drilling fluid. Particularly, the surge pressure reduction system of the ""881 patent includes a diverter device connected between a drill pipe and a drilling/production liner. The diverter device has a housing assembly with a set of flow holes and an axial bore formed therein. A sliding sleeve resides within the axial bore of the housing assembly. When the sliding sleeve is positioned above the set of housing flow holes such that the sleeve does not block the set of flow holes, communication is established between the axial bore of the housing assembly and the annular space between the housing assembly and the borehole. This is called the xe2x80x9copen port positionxe2x80x9d and is established to facilitate surge pressure reduction when running a drilling/production liner through drilling fluid down a borehole. When the sliding sleeve is displaced axially downward such that the set of flow holes of the housing assembly is blocked by the sleeve, communication is interrupted between the axial bore of the housing assembly and the annular space between the housing assembly and the borehole. This is called the xe2x80x9cclosed port positionxe2x80x9d and is established to provide circulation of drilling fluid downward through the diverter device and to the bottom of the drilling/production liner without short-circuiting the flow of drilling fluid through the set of flow holes of the housing assembly. The closed port position is also established to facilitate cementing operations when the drilling/production liner reaches total depth of the borehole.
The diverter device disclosed in the ""881 patent includes an indexing mechanism to facilitate shifting the sliding sleeve axially downward from the open port position to the closed port position. The indexing mechanism of the ""881 patent includes: (1) a yieldable ball seat attached to the sliding sleeve to receive a drop ball, (2) a set of latching fingers formed on the sliding sleeve, (3) an upper groove formed on the inner wall of the housing assembly to receive the latching fingers of the sliding sleeve in the open port position, and (4) a lower groove formed on the inner wall of the housing assembly to receive the latching fingers of the sliding sleeve in the closed port position.
In operation, a drilling/production liner is run down a borehole using a drill pipe and a surge pressure reduction tool attached between the drill pipe and the drilling/production liner. Initially, the tool is set in the open port position to provide surge pressure reduction functionality while the tool is being lowered through drilling fluid down the borehole. In the open port position, the latching fingers of the sliding sleeve engage the upper groove in the housing such that the sliding sleeve does not inhibit communication via the set of flow holes of the housing.
As the drilling/production liner is lowered in the open port position, the drilling fluid flows upward through the drilling/production liner, into the tool, and outward into the annular space between the tool and the borehole via the set of flow holes. Once total depth is achieved, the surge pressure reduction tool must be in the closed port position to facilitate hanging and cementing operations. Therefore, a drop ball is released into the drill pipe to land in the yieldable ball seat thereby effectively sealing the sliding sleeve. Drilling fluid pressure is then increased above the drop ball to disengage the latching fingers from the upper groove of the housing assembly and shift the sliding sleeve axially downward into the closed port position where the latching fingers engage the lower groove of the housing assembly. Drilling pressure is once again increased above the drop ball to push the ball through the yieldable ball seat and out of the bottom of the drilling/production liner.
U.S. application Ser. No. 10/051,270 (xe2x80x9cthe ""270 applicationxe2x80x9d), which is incorporated herein by reference and which should be referred to with respect to the advantages provided by that invention, also discloses a diverter device with an indexing mechanism employing latching fingers. However, the ""270 application also describes the principle of operation of a surge pressure reduction apparatus having a volume compensation device.
The volume compensation device of the ""270 application provides a solution to problems observed during the running downhole of a drilling/production liner where the liner becomes plugged with drill cuttings and debris. Oftentimes, these drill cuttings and debris are created and left in the borehole during drilling operations. If the drilling/production liner becomes plugged while being run downhole, it may not be possible to shift the sliding sleeve downward into the closed port position. Therefore, with the sliding sleeve unable to shift out of the open port position, cementing operations cannot be performed at total depth and circulation operations cannot be performed if the drilling/production liner encounters a tight hole condition. This is due to a pressure build-up in the drilling fluid trapped between the yieldable ball seat sealed by the drop ball and the debris blocking the drilling/production liner. This pressure build-up causes a hydraulic lock condition in which the trapped drilling fluid resists the force exerted above the drop ball to shift the sliding sleeve axially downward. Therefore, the tool cannot be shifted out of the open port position and communication between the surface and the drilling/production liner via the drill pipe is short-circuited by the open set of flow ports of the tool.
A volume compensation device in accordance with the ""270 application may be used to permit the surge pressure reduction tool to be shifted to the closed port position thus facilitating cementing operations and circulation of drilling fluid even in the event that the drilling/production liner becomes plugged with drill cuttings or downhole debris. The volume compensation device is connected between the drilling/production liner and the diverter device; and, when activated, the volume compensation device accumulates a volume of drilling fluid which is equal to or greater than the volume of drilling fluid displaced when the sliding sleeve moves from the open port position to the closed position.
While the inventions of the ""881 patent and ""270 application provide for more efficient running of drilling/production liners downhole, it has been observed that under certain conditions the indexing mechanism of these prior diverter tools may not function properly to shift the sliding sleeve into the closed port position. There are several reasons for this shifting problem. First, the latching fingers of the indexing mechanism were designed to release and shift the sleeve at low pressures (e.g., 200-300 psi), thus reducing the flexibility of the tool. Also, if the latching fingers of the indexing mechanism were installed in a position high in the housing, then atmospheric pressure is trapped between the lowest two sets of seals. Thus, when the tool is run downhole with the latching fingers in this position, the differential pressure between hydrostatic pressure and the atmospheric pressure creates a xe2x80x9chydraulic lockxe2x80x9d condition thus preventing the tool from functioning properly. Another reason for the potential shifting problem is that the seals between the sliding sleeve and the housing assembly of prior diverter devices have been installed on the sleeve rather than on the housing assembly. Thus, the seals cross the housing flow holes during shifting of the sliding sleeve and the seals are exposed to debris and contaminates in the borehole which can damage the seals.
Accordingly, the oil well industry would find desirable a surge pressure reduction tool having a more reliable and easier to assemble indexing mechanism to shift the tool from the open port position to the closed port position.
In accordance with the present invention, a method and apparatus for reducing surge pressure while running a drilling/production liner or sub-sea casing on a drill pipe with a running tool through drilling fluid down a borehole using a drilling rig is provided. While the present invention is described with respect to running a xe2x80x9cdrilling/production linerxe2x80x9d downhole, it should be understood that the present apparatus and method may also be used for running a xe2x80x9csub-sea casingxe2x80x9d downhole.
The surge pressure reduction apparatus in accordance with the present invention includes a diverter device connected between the drill string and the drilling/production liner. The diverter device functions to: (1) facilitate surge pressure reduction when running a drilling/production liner through drilling fluid down a borehole, and (2) provide circulation of drilling fluid through the drilling/production liner to free the drilling/production liner and to facilitate cementing operations once total depth is reached.
In a preferred embodiment, the diverter device of the present invention includes a housing assembly with a set of flow holes formed therein. The housing assembly is suspended from a drill pipe such that the drill pipe provides a communication conduit between the drilling rig on the surface and the borehole. The diverter device further includes a sleeve positioned within the housing assembly and having a set of flow ports formed therein. When the set of flow holes of the housing assembly is aligned with the set of flow ports of the sleeve, the tool is in an xe2x80x9copen port position.xe2x80x9d When the set of flow holes of the housing assembly is blocked by the sleeve, the tool is in a xe2x80x9cclosed port position.xe2x80x9d The diverter device of the present invention still further includes an indexing mechanism for moving the sleeve from the open port position to the closed port position. The indexing mechanism includes: (1) a yieldable ball seat attached to the sleeve for receiving a drop ball, (2) a circumferential groove formed along the outer wall of the sleeve and near the upper end of the sleeve, (3) a spring ring installed in the circumferential groove of the sleeve, (4) a circumferential groove formed on the inner wall of the housing assembly to receive the spring ring when the sleeve shifts to the closed port position, and (5) a shear ring and a set of shear pins to hold the sleeve in the open port position. To shift the sliding sleeve axially downward into the closed port position, the drop ball is released into the yieldable seat and drilling fluid pressure is increased above the drop ball to shear the set of shear pins from the shear ring. The quantity of shear pins governs the pressure at which the sleeve is shifted. Accordingly, the indexing mechanism of the present invention can be assembled to shift at a pressure as low as 150 psi to as high as 1400 psi. Once released from the set of shear pins, the sliding sleeve moves axially downward until the spring ring engages the circumferential groove of the housing assembly to lock the sliding sleeve in the closed port position.
The surge pressure reduction apparatus in accordance with the present invention may also include a volume compensation device connected between the diverter device and the drilling/production liner. The volume compensation device, when used, accumulates a volume of drilling fluid which is equal to or greater than the volume of drilling fluid displaced when the sliding sleeve moves from the open port position to the closed position.
In one preferred embodiment, the volume compensation device includes a housing having an upper end and a lower end and an axial bore formed therethrough. Additionally, the housing includes a set of flow ports formed therein near the upper end. The volume compensation device also includes an inner sleeve having an upper end and a lower end, and an outer diameter smaller than the diameter of the axial bore of the housing. The total length of the inner sleeve is less than the length of the axial bore of the housing. The inner sleeve is arranged within the axial bore of the housing, and the upper end of the inner sleeve is attached to the upper end of the housing to form an annular space between the inner sleeve and the housing. An annular piston having an inner diameter approximately equal to the outer diameter of the sleeve and an outer diameter approximately equal to the diameter of the axial bore of the housing is attached to the lower end of the sleeve by at least one shear pin. If the drilling/production liner becomes plugged with drill cuttings or downhole debris, then trapped drilling fluid pressure within the volume compensation plug applies an upward force against the annular piston such that the set of shear pins shear and the annular piston moves axially upward. This provides the apparatus of the present invention with additional volume as required to shift the diverter device to the closed port position.
In the open port position, apparatus in accordance with the present invention provides an alternative flow path for drilling fluid to flow upward from the borehole into the tubular member, from the tubular member to the running tool, from the running tool to the volume compensation device, from the volume compensation device to the diverter device, and from the diverter device out into an annular space between the drill pipe and the borehole via the set of housing flow holes. Providing this flow path facilitates surge pressure reduction when lowering the tubular member downhole through drilling fluid.
In the closed port position, apparatus in accordance with the present invention provides a flow path for drilling fluid to flow downward from the drill pipe to the diverter device, from the diverter device to the volume compensation device, from the volume compensation device to the running tool, from the running tool to the tubular member, and from the tubular member out into the borehole. Providing this flow path facilitates circulation and cementing operations.
In another embodiment of the present invention, the diverter device includes a seal installed on the inner wall of the housing assembly above the set of housing flow holes and a seal installed on the inner wall of the housing assembly below the set of housing flow holes. Since the seals are fixed to the housing assembly rather than to the sleeve, the seals never cross the set of housing flow holes and thus are not exposed to debris and contaminants in the borehole that could damage the seals. Moreover, this arrangement of the seals prevents a hydraulic lock condition from forming when the sleeve is shifted to block the set of flow holes of the housing assembly.
The apparatus of the present invention is an improvement over prior art diverter devices for at least the following reasons: (1) it provides a more reliable indexing mechanism to shift the diverter device, and (2) it reduces the possibility of misassembly by shop personnel.